This invention relates generally to melt-blown materials, and more particularly concerns a melt-blown nonwoven wiper consisting of a composite web made up of layers of melt-blown fibers. The layers have different fiber and pore sizes resulting in a pore size distribution across the thickness or Z-direction of the web. The pore size distribution is tailored to optimize liquid pick up rate and liquid holding capacity of the wiper.
The melt-blown nonwoven wipers are well known in the art and find utility as disposable industrial wipers in numerous manufacturing and maintenance facilities where personnel find it necessary to wipe up oil, grease, and water from a variety of surfaces. Such nonwoven wipers generally consist of a web of melt-blown thermoplastic fibers. One such wiper made of melt-blown polypropylene fibers is sold by the assignee of the present invention under the trademark Kimtex.
Melt-blown nonwoven wipers have the advantage over cloth wipers of being cost effectively disposable and providing similar wiping characteristics to cloth. Particularly, all industrial wipers must be able to quickly pick up spilled liquids. both oil based or water based, and leave a clean streak free surface. In addition, the wipers must have a sufficient capacity to hold such liquids within the wiper structure until it is desired to remove the liquids by pressure such as by wringing.
As a practical matter, a nonwoven industrial wiper will be judged in terms of performance with respect to traditional nondisposable, woven cotton shop towels. In that regard, it is necessary to design a nonwoven industrial wiper so that its performance characteristics approach those of the traditional woven shop towel while providing cost effective disposability of the nonwoven industrial wiper. In the past, nonwoven industrial wipers have not been able to provide the same desired performance as woven shop towels, particularly, in terms of the rate of pick up of oil and water and the holding capacity for both oil and water. Moreover, such deficiencies of nonwoven industrial wipers are particularly troublesome because there appears to be an inverse relationship between the holding capacity of the nonwoven industrial wipers and the rate of pick up. In other words, in order to increase holding capacity, it has in the past been thought that it was necessary to sacrifice the rate of pick up. Likewise, in order to improve rate of pick up, it was thought necessary to sacrifice some holding capacity.